Designing a new secondary school to Passivhaus
Was it a Passivhaus school from the outset?
It’s part of a large scheme on two neighbouring schools. During the planning design (Stage C) the Architect was looking for alternative ways of achieving the London Borough of Camden Carbon reduction targets. We undertook a feasibility study to show that by going further to reduce energy use on the new parts of the scheme a smaller energy centre and solar PV installation could be used. The target for energy efficiency was formalised by targeting the Passivhaus standard.
Sounds like it might have meant some big changes to the design?
There were some small changes needed, but the scheme has a good South facing aspect and already had a fairly small exposed surface area compared to its size. We made recommendations to change the structure away from a steel frame – which bridged the insulation in a number of places – and to optimise the façade design to reduce the amount of glass. Thankfully it was all accepted and even meant a cost saving over the original cost plan. We were appointed as Passivhaus consultants for the detailed design phase.
You had to reduce the glass to the classrooms, doesn’t this make it darker inside?
In theory, but it won’t be noticeable. We worked hard with the Mechanical Engineers to model the daylight in the classrooms. Most of the reduction was found by getting rid of windows near the edges of the room or at low level that don’t contribute much to daylight inside. The area was also affected by how many opening windows we need to give enough ventilation to the classroom in summer. The students give off a lot of heat when they’re working hard.
I thought Passivhaus had to use mechanical ventilation?
It does, but opening windows allow the teachers to control their own classroom without having a complicated control panel. The fans provide the background ventilation for fresh air and to remove odours and moisture, particularly in the winter, but in the summer the amount of air needed is much higher. The two systems work well together.
Right, sounds simple. Where has the project got to now?
It has received planning consent and gone to tender. The challenge starts here as Passivhaus is very dependent on construction quality and delivery. We put together very detailed information to help the contractor and look forward to seeing the project delivered.